1. Field of the Invention
The present invention relates to surgical sutures and their production. In particular, the invention relates to surgical sutures and apparatus for the attachment of surgical needles to surgical sutures.
2. Description of Related Art
In the past, surgical needles with an eye for reception of the suture have been used. As in conventional sewing, the thread is sometimes doubled through the eye of the needle. The doubled end of the thread in the eye must pass through tissues during use, which enlarges the opening made in the tissue. This leads to loss of tightness and increased trauma. Due to this problem, there has been a trend towards eyeless needles in which the end of the suture is attached to the needle so that the suture is pulled through the tissue thus minimizing the opening and causing a minimum of trauma.
The most common surgical suture of this type is a single-use needle of appropriate size and shape which is crimped to the end of the suture, so that the needle is used once and then discarded. The attachment can be accomplished by use of a "drilled end" needle; that is, one in which a concentric aperture is formed in the end of the needle in which the suture is placed and the needle crimped around the suture. Alternatively, a "flanged" needle may be utilized in which a U-shaped channel is stamped into the end of the needle with the ends of the "U" being crimped about the suture to hold the suture together.
The attachment must be one which is: predictably secure; causes a minimum of damage to tissue; is convenient for the using surgeon.. permits sterilization; and entails reasonable costs. In addition, the attachment must withstand the rigors of manufacture, sterilization, storage, shipment and use.
During use, it has been found that upon completion of the stitching procedure by the surgeon, it is convenient for the surgeon to be able to readily detach the needle from the suture thus permitting the end of the suture to be tied or otherwise secured. The needle may thereafter be removed from the work area so as to avoid harm to the patient, surgeon and other personnel. Cutting the suture with scissors or a scalpel is a convenient method of disengaging the needle but requires an extra instrument and an extra manipulation.
More recently, techniques have been developed to attach the suture to the needle in a manner which permits the surgeon to readily separate the components by merely tugging at the needle at the end of the stitching procedure.
The pull required for tugging the needle from the suture is referred to in the U.S. Pharmacopeia as "needle-attachment" or "testing the security of attachment of eyeless needles to sutures". For convenience, the term "pull-out" is used.
Experience and testing procedures have determined that the pull-out must be at a sufficiently high value that the suture may be placed without risk of the needle becoming detached from the suture during placement; and yet it must pull-out at a value far below the breaking strength of the suture and will predictably pull-out before the suture breaks. In addition, the suture must pull-out at a value which is reasonably exertable upon the needle by the surgeon at the time of use.
Conventional crimp operations are difficult to control. Usually a crimp is created between several dies which close to a fixed gap. Any variation in: the crimping dies, the needle size, the hole size, or the suture size alters the degree of crimp. However, with such techniques, the variation can be larger than is acceptable in the manufacture of controlled release or controlled pull-out sutures.
The conventional crimping method requires that the back end of the needle be struck with two half moon shaped dies. The needle is then rotated 90.degree. and the dies are arranged to strike the needle a second time. In effect, the first strike changes a round hole into one of eliptical shape, i.e., major and minor axes. The act of rotating the needle 90.degree. and repeating the operation to some extent, causes the minor axis to become its counterpart, and the major axis to become the minor axis thereby completing the attachment in a relatively uniform manner. The effect of this procedure is to distort the end of the needle thereby causing it to lose its symmetry. This last mentioned disadvantage results in corresponding assymmetry of tissue apertures during use.
The diameter of the suture, the diameter of the needle, the concentricity of the aperture in the needle, the outside diameter of the needle, the braid size of the suture, coating material, time and concentration of baths, and drying conditions are all extremely critical in predicting and controlling the pull-out force. In addition to size effects, the surface smoothness of the suture and the needle aperture, and lubricants on either components affect the pull-out values. The conventional method of crimping, as described, underscores many of these parametric inconsistencies and necessarily utilizes multiple hits to overcome these process variabilities.
To date, techniques devised for connecting such suture components in a manner to perform within the preferred guidelines are not effective in maintaining needle symmetry and uniformity of dimensions, particularly with a single hit. The present invention avoids the aforementioned disadvantages and provides a die and a method for attaching surgical sutures to needles in a controlled manner while retaining the symmetry of the needle, all with less time and expense.